UK Natural Capital: Experimental carbon stock accounts, preliminary estimates

Geocarbon

Scope and classifications

In these accounts a spatial definition of the UK consistent with the UK continental shelf has been adopted¹. It includes all resources located within the UK’s exclusive economic zone (EEZ)² as well as on-shore deposits. This commonly used definition is also adopted by the UK Oil & Gas Authority³ (OGA), facilitating consistency with this and a wide range of other data sources.

SEEA Central Framework categorises mineral and energy resources into three classes – Class A: Commercially Recoverable Resources, Class B: Potentially Commercially Recoverable Resources and Class C: Non-Commercial and Other Known Deposits. SEEA Class A reserves could broadly be categorised as within the OGA’s proven and probable reserves classification. The scope excludes potential deposits where there is no expectation of them becoming economically viable and there is a lack of information to determine the feasibility of extraction or to have confidence in the geologic knowledge (SEEA-CF, UN et al 2014b, para 5.179).

The focus of this work is the carbon stored in, as opposed to the economic viability of, the respective geocarbon resources. As such, when determining scope this work adopts the broadest measure available of the respective geocarbon resources, while still attempting to align as close as is possible to SEEA concepts. Hence uneconomic resources are included when calculating estimates of geocarbon.

Data Sources

Oil & Gas

The OGA provides the most comprehensive selection of data on UK oil and gas stocks. The estimates for oil and gas are split into reserves, potential additional resources (PARs) and undiscovered resources. The OGA definition of reserves can be disaggregated into proven, probable and possible. PARs exist in discoveries for which there are no current plans for development and which are not currently technically or commercially producible (DECC, 2015). Methodology for estimating undiscovered resources combines mapped leads data from OGA with mapped prospects data from private oil companies. For areas where there is insufficient mapping of leads and prospects, an estimate is made based on knowledge of its respective geology (DECC, 2015). OGA give an upper and lower limit for estimates of undiscovered oil and gas reserves; this study uses the simple average of the two. It should also be noted that the factors which determine the commercial viability of the stock will also influence carbon content (i.e. deeper reserves are harder to extract, but hold a richer carbon content). This would apply to all geocarbon resources. Additional information on this will prove useful in the future.

While the UK Continental Shelf’s reserves’ categorisation is different to SEEA Central Framework, SEEA Class A reserves could broadly be categorised as proven and probable reserves. This is the approach employed in this article.

Coal

Coal data used in this article is sourced from the German Federal Institute for Geosciences and Natural Resources (BGR) with a 2013 reference year. The BGR: Reserves, Resources and Availability of Energy Resources study presents data on the proportion of coal resources held by the top 20 countries (by volume of reserves) across the world. Most pertinent to the carbon accounts is that the estimates are separated into hard coal⁴ and lignite resources enabling more accurate, although still imprecise, estimation of the respective carbon content of UK coal resources.

The Department of Energy and Climate Change (DECC) also produces 2013 stock estimates of the coal resources for Great Britain (GB) in its Identified GB Coal Resource Assessment. This data are broken down into two broad categories: underground mining and surface mining, which are further disaggregated by current mines and licences, and prospects. A regional breakdown is also available⁵, which may prove useful when attempting to derive carbon content of different coal deposits across the region. However, the lack of a breakdown by type of coal⁶ means the format of this data is less useful for the purposes of this article.

Shale

Geographic surveys suggest that the UK has substantial shale gas resources (UK Economic Affairs Committee). The 2010 BGS/DECC Shale Gas report and the 2014 UK data and analysis for shale gas prospectivity report identified significant potential shale development areas across the country. While the carbon content of these deposits could have a significant impact on UK carbon stocks, the fledgling nature of the industry means the availability of data are currently limited. The current set of carbon accounts does not include estimates for shale, although this will be an area for future research.

Limestone and other carbonate rocks

Deposits of limestone and other forms of carbonate rocks are widely distributed across the UK. However, differences in the respective chemistry and thickness means the carbon contents may vary considerably. Related stock data on the extent of such deposits is limited for the UK and is, therefore, not currently included.

ONS Environmental Accounts has published statistics on annual rates of domestic extraction for limestone, chalk and dolomite. However, at present flow data on chalk and dolomite is aggregated, while limestone statistics include gypsum making the identification of resource specific carbon content problematic. This is another area which requires further work and research in order to present meaningful statistics.

Changes in geocarbon stocks

Additions to stock for any specific category can take place in various ways. Firstly, there are reclassifications between forms of stock where reserves become commercially viable as a result of market forces, or changes in technology, (for example, PAR reserves could be upgraded to proven reserves, meaning a reduction in one reserve category is matched by an increase in another). Secondly, as existing reserves are reassessed using improved techniques, the content of the reserves may be subject to upwards reappraisal. Thirdly, new reserves may be discovered.

Conversely, reductions in oil or gas stocks can happen in the following ways. Firstly, managed reductions reflect the extraction of these reserves for consumption. The final two entries are the opposite movements from the first and second forms of additions to stock outlined above. A reclassification may have a negative impact on a particular stock where it results in a shift away from that stock; and as existing reserves are reassessed using improved techniques, the content of those reserves may be subject to downwards reappraisal although this may not be simultaneous⁷.

There is currently only limited data available on additions to, and reductions in, UK geocarbon stocks. As part of the UK Environmental Accounts, we publish a material flow dataset which records the total mass of natural resources and products that are used by the economy. The Material Flow Account (MFA) draws on a range of primary data sources to populate its respective tables including: BGS for mineral flows, and Defra for flows related to agricultural products. While this includes broad based data on geocarbon resource categories for both fossil fuels and carbonate rocks, the aggregated structure of the data means it is not currently compatible with the stock estimates.

DECC publishes partial information on annual flows of oil and gas in its annual Digest of UK Energy Statistics (DUKES) report. Furthermore, BGR publishes data on UK coal production, together with its UK coal stock estimates. Retaining the same source for both stock and flow data allows for changes to the stock to be presented on a consistent basis over a given time period.

Unfortunately no information is available on the extent of changes to stocks resulting from reclassifications or discoveries. As a result, with the exception of flows from extraction/production (managed contraction), all other changes in stock are attributed to upward/downward reappraisals.

Carbon conversion factors

Carbon conversion factors allow for the physical volume of a given geocarbon stock to be converted into estimates of its respective carbon mass.

The carbon richness of a given geocarbon resource can vary dependent on their respective geological location. For instance, the pressure and temperature to which geocarbon stocks are exposed when in situ means their respective carbon contents can vary considerably, both between and within geocarbon categories. Table 2 presents a list of the carbon conversion factors for the respective components of geocarbon.

Oil

In its natural state, crude oil ranges in density and consistency from very thin, light weight and volatile fluidity to an extremely thick, semi-solid heavy weight oil (Chevron, n.d.). A breakdown of the types of crude oil contained within the UK continental shelf could not be found. A broad based study on carbon emissions from different fuels published by Biomass Energy Centre (BES) suggests that oil has a carbon content of around 85%⁸. While BES provides only limited detail on the method used to reach this estimate, it will be used in this study as it does correspond with the 85.5% crude oil carbon content weight used by Ajani & Comisari, 2014. However, the limited account given to spatial variation across deposit sites suggests the margins for error arising from the use of this approach are relatively broad.

Gas

OGA data separates gas reserves into three categories: dry gas, condensate field gas and associated gas. Like oil, information on the carbon content of the respective gas subdivisions is limited. The US EPA suggests that based on a weight of 0.714 kilograms (kg) per cubic metre, natural gas has a carbon mass of 0.5262 kg, or 74%. However, as with oil, the carbon intensity of natural gas is likely to vary with the depth and pressure of the deposit. The Biomass Energy Centre (BEA) has published estimates suggesting that the carbon content of natural gas is slightly higher at around 75% rich. Unfortunately, there is no information provided by BEA on the methodology underpinning this rate, however, it does concur with the ratio used by Ajani & Comisari, 2014 for categories of natural gas⁹ .This underpinned the decision to use the BEA rate in carbon content calculations.

The estimation of the carbon stored in gas resources is calculated by the following steps:

One cubic metre of natural gas weighs 0.714 kg, which assumes a 75% carbon content:

1 cubic metre of natural gas = 0.714 kg 0.714 * 75% = 0.5355 kg

Coal

The carbon content of coal varies not just by the class of coal (lignite, sub-bituminous, bituminous and anthracite), but within each class (Ajani and Comisari, 2014). During the coalification process¹⁰ the carbon content increases from as little as 15% in lignite¹¹ to as much as 95% in anthracite (BGS, 2010). To gather information containing this level of detail, extensive sampling across the UK to determine the carbon content of different coal deposits would be required. Unfortunately, such information is not readily available so this work is restricted to applying conversion factors for tonnes of coal to tonnes of carbon that are indicative only.

The coal resources presented in these accounts have been grouped into the categories: hard coal and lignite (brown coal). Hard coal comprises the aggregated stocks of sub-bituminous coal, bituminous coal and anthracite (BGR, 2014).

A range of sources have been consulted to determine suitable conversion factors. For hard coal, average carbon content estimates range from 63%¹²to as much as 85%¹³.This work draws on the BEA estimate and applies an average carbon content for hard coal of 75%. The carbon content of lignite has been sourced from the US Energy Information Administration (EIA) and estimated to be 30%, which is the middle of the EIA range for lignite.

Biocarbon

Scope and classifications

The primary data source used to populate the biocarbon stock account is the Countryside (CS) Survey for 1998 and 2007. Conducted by the Centre for Ecology and Hydrology (CEH), the CS Survey is a long-term scientific study used to inform decision makers and the public on the status of the managed and natural UK environment, including soil carbon stocks and vegetation composition (Ostle, 2009). The CS Survey classifies its ecosystems by Priority¹⁴ habitats, which are linked directly the Broad Habitat classifications used in the UK National Ecosystem Assessment (NEA). The NEA’s approach to classification supports the identification and measurement of terrestrial, freshwater and marine ecosystems contained within eight collections of "broad habitat" types (NEA, 2016). The NEA Broad Habitats largely align with the SEEA-EEA provisional land cover classifications (SEEA-EEA, p.60), which uses a system based on the physical cover of the Earth’s surface.

Biocarbon flows between 2008 and 2014 have been inferred using the land use, land use change and forestry (LULUCF) data produced by DECC within its UK Greenhouse Gas Inventory. DECC data are compiled based on a land use Classification, which accords to the Intergovernmental Panel on Climate Change (IPCC) reporting guidelines.

The CS Broad Habitat classes were mapped to the SEEA-EEA nomenclature using guidance within the Land Cover Accounts. This process enables average carbon content per hectare by habitat figures to be combined with SEEA-EEA consistent land cover data for the UK. Separately, IPCC Land Use Classifications were mapped to SEEA-EEA classifications using guidance provided by Weber (2014). Both revised habitat classifications were then adapted to the UK context. The concordance tables used to map the CS Broad Habitat classes and IPCC Land Use Classifications to the SEEA-EEA nomenclature are presented in Appendix 3.

Data sources

Terrestrial habitat soils

Soil is a major component in the global carbon cycle and vulnerable to impacts from human activity. Thus, even small rates of carbon loss from soils can have significant consequences for the overall carbon budget and, in turn, atmospheric CO2 concentrations (Dawson and Smith, 2006).

The majority of organic carbon in terrestrial ecosystems is stored below ground (Janzen, 2004). As a result, stock estimates of soil carbon vary depending on the depth of the soil considered. The most disaggregated and up to date soil carbon stock estimates are contained in the CS Survey, which records tons of carbon per hectare in Great Britain. Estimates for the total soil carbon stock of each Broad Habitat in the UK have been produced by combining the tonnes per hectare by habitat units, with land area estimates from the Land Cover Accounts.

Limitations on the scope of the CS survey mean estimates need to be supplemented with data from additional sources in order to present a fuller picture of soil carbon stocks across the UK. A key limitation of the CS survey is that it only reports on soils to a depth of 15cm. Peat depth varies on average between half a metre and three metres, although depths of up to eight metres are not uncommon (SNH). Limiting estimates of carbon stored in UK peat resources to a soil depth 15cm would, therefore, result in a significant underestimate and represent a major omission. This would have greatest impact on estimates for Scotland (Ostle et al, 2009).

The compilation of accurate volume estimates of UK peat resources requires information on: the extent and condition of peat resources; the depth of peat resources; and the carbon composition per unit volume of peat. There have been several attempts to undertake this since the 1990s. Milne and Brown (1997) provide carbon values for peat within Great Britain to a depth of four metres. For Scottish peatland resources, the authors assume carbon densities increase with depth. DECC uses the biomass carbon density for each land type from this study¹⁵ when estimating changes in biocarbon stocks due to land use change in its annual Inventory of Greenhouse Gas Emissions (CEH, 2010). However, only limited information is available on how changes in bulk density were calculated. Furthermore, Milne and Brown (1997) do not separate figures for peat from other soil types in England and Wales.

The most up-to-date overview of data sources on UK peatland is Defra’s Scoping the Natural Capital Accounts for Peatland study. However, while the report includes comprehensive information on the extent and condition of peatland resources across the UK, it provides only limited information on peat depth and bulk densities under the rationale that: ‘as depth of peat soil is not usually known with accuracy, and many peat soils extend significantly deeper than this, any depth estimate is only a guide for those identifying the presence of peatlands (p.10)’.

This Carbon Account uses the work of Billet et al. (2010)¹⁶ ,which draws on a range of separate country centric studies to produce a total stock estimate for the carbon stored in peatland resources across the UK. For carbon estimates up to one metre in depth, Chapman et al. (2009)¹⁷ is used for Scotland, while Bradley et al. (2005)¹⁸ is used for England, Wales and Northern Ireland. For carbon estimates in excess of one metre in depth, Chapman et al. (2007) is used for Scotland, Smith et al. (2007)¹⁹ is used for Wales, while estimates for England and Northern Ireland use Scottish data to produce pro rata estimates.

Peatland assets fit within the SEEA-EEA Open wetlands ecosystems classification. In line with the Freshwater Ecosystem Assets and Services Accounts, all peatland assets are allocated to the Bog subcategory of the Open wetlands Broad Habitat.

Finally, soil carbon stocks beneath UK woodland resources have been supplemented by using data from the Forestry Commission’s (FC) 2012 report Understanding the carbon and greenhouse gas balance of forests in Britain. The FC uses results from the BioSoil Survey²⁰ ,which describes and samples soils down to a one metre depth on a 16x16 km grid network that fall onto forested land. The report provides a figure for the average carbon stored in soil per hectare of UK woodlands. It does not, however, distinguish between different classes of woodland i.e. conifer or broadleaf.

Terrestrial habitat vegetation

Estimates of vegetation carbon by Broad Habitat are primarily sourced from Natural England’s Carbon storage by habitat, which itself draws on Ostle et al, 2009 to estimate carbon stocks per hectare for the UK. These are combined with ONS estimates of UK land cover to create estimates for carbon stock in vegetation by habitat based ecosystem.

The ecosystem subcategories of Coniferous forest, and Broad leaf, mixed and yew woodland have been populated using more accurate data from the FC’s National Forest Inventory report on the carbon content of British woodland. Estimates are based on a broad definition of Woodland carbon as: “comprising carbon stored in all living plant material in both the above and below ground parts of trees (including major roots, stumps, stems, branches, twigs and foliage) in stands with a mean diameter (at breast height) of 7 cm or more” (p.2).

Finally, the exclusion of vegetation carbon data for the Fen, marsh and swamp habitat classification means the total biocarbon stock figure is an underestimate. This could be an area for future research.

Coastal margins

Coastal margin ecosystems can occur in both terrestrial and marine habitats simultaneously, which creates double-counting problems. For instance, other habitats or land cover categories, e.g. grassland or urban areas, can be situated on what would be called “the coast” (ONS, 2016). To avoid potential issues with double-counting, this article presents carbon stock information related to Coastal margin habitats separate from the terrestrial habitats.

The SEEA Central Framework classifies ‘coastal water bodies and intertidal areas’ as “defined on the basis of geographical features of the land in relation to the sea (coastal water bodies, i.e., lagoons and estuaries) and abiotic surfaces subject to water persistence (intertidal areas, i.e., coastal flats and coral reefs)”.

The UK NEA defines six main habitat sub-classes as coastal: Sand dunes, Machair, Saltmarsh, Shingle, Sea Cliffs and Coastal Lagoons. This includes small islands, sand and shingle beaches, but excludes coastal grasslands, mudflats, rocky shores and estuaries, and coastal urban areas. Sand dunes, saltmarsh and machair comprise over 90% of the UK Coastal margin habitat (Beaumont et al., 2014).

Coastal margins produce significant benefits in terms of carbon storage and carbon sequestration. Basic quantification of the carbon pools stored in coastal margins is difficult. This is in part because of a grey area between coastal margins and the marine environment, meaning they are commonly grouped together (ONS, 2016), but also because the coastal margins constitute a narrow zone of land, which are not a distinct habitat. As such, in many cases data gathering does not differentiate between key aspects. Furthermore, coastal habitats were excluded from the 1998/2007 CS Surveys due to a lack of representative coverage.

The UK NEA provides estimates for the carbon stored in UK Coastal Margins. Drawing on CEH data it estimates coastal margins vegetation and soils combined to hold at least 7.24 MtC carbon (UK NEA (2011), Chapter 11). While this figure underestimates the carbon storage component in Saltmarsh soil²¹, where soil depth remains largely unquantified, it is broadly in line with the Beaumont et al. (2010) estimate of 6.8 MtC held in UK coastal margin vegetation and soils.

This article uses the soil carbon stock average estimate for Coastal margin habitats published in Natural England (2012), which is combined with the 2007 SEEA-EEA Land Cover estimate for Coastal margins habitats.

While this produces a higher estimate than the combined vegetation and soil carbon figure reported in UK NEA (2011), this still only represents a partial estimate, since the land cover data for coastal margins only includes certain habitat sub-classes.

Open waters

Open waters form part of the UK NEA Freshwaters Broad Habitat classification. The Open waters sub-class broadly matches up with the SEEA-EEA based habitat class: Inland water bodies. Open waters can be further subdivided into two categories: standing waters²² and flowing waters²³(ONS, 2015). Wetlands act as transitions between terrestrial and open water systems.

Information on the carbon stocks in, and flows to and from, open water ecosystems form an important aspect of this field of analysis. Deposition of organic sediments within lakes, ponds and reservoirs is an important component of the carbon budget (UK NEA: Chapter 9).

There is currently a lack of data to quantify the total stock of carbon stored within the UK aquatic environment, and it is therefore excluded from the analysis at this stage. We will look to investigate this during the next process to update the ONS Freshwater Ecosystems Account.

Changes in biocarbon stocks

Terrestrial ecosystems

The delivery of ecosystem services by the UK’s natural environment can have a significant impact on the stocks of carbon stored within its respective habitats. For instance, the delivery of provisioning services, such as the removal of timber to support economic activities, can result in a reduction in the carbon stocks held within woodland habitats, coupled with an equal increase of carbon in the inventories of timber in the economy (see Section 4). Conversely, the delivery of regulating services, such as carbon sequestration²⁴, can be reflected as an addition to vegetation carbon stocks held by the respective UK habitat class.

The data set used in this work does not allow for separation between ecosystem services. Furthermore, a given habitat’s ability to provide ecosystem services is significantly influenced by its condition. However, a lack of suitable information means habitat condition is not factored into estimates at this time. Finally, we are unable to separately identify additions to, and reductions in, stocks at this stage so changes are presented on a net basis.

Ideally, the best approach to measure changes in carbon stocks between reference periods would be to use the data on carbon flows from the land use, land use change and forestry (LULUCF) sector reported by DECC as part of its annual UK Greenhouse Gas Inventory publication. Unfortunately, LULUCF data does not contain the appropriate level of detail required for use within the carbon stock account. This will be an area which would benefit significantly from closer collaboration with our colleagues in DECC. Section 3.6 below provides further detail on the adjustments required as well as some broad aggregate estimates on carbon flows when using a LULUCF based approach.

The Land Cover accounts show estimates by SEEA-EEA-based habitat classes for the years 1998 and 2007. The CS Survey also contains estimates for GB of changes in carbon soil content by terrestrial habitat between 1998 and 2007. These are presented in Appendix 4. By combining the two data sets, estimates for the change in soil stocks by habitat can be generated.

Exceptions to this relate to estimates of changes on soil carbon content gathered from sources outside of the CS survey. For instance, the data sources used to support estimates of soil carbon in the woodland, and the bog (peat) habitat classes did not include information on changes in the soil content. Thus, in cases where change data was unavailable, movements in the carbon stock of the respective habitats are based only on land cover changes between 1998 and 2007. The same applies to all estimates for the carbon content of vegetation, including those sourced from the CS Survey. Data was only available for one reference year. Therefore, the average vegetation carbon content for all habitats is assumed to have stayed constant over the 1998 to 2007 reference period. Again, any changes are based solely on land cover.

Coastal margins

The Coastal margins scoping study (ONS, 2016) presents an extensive overview of potential data sources that could report on carbon stock changes related to coastal margin habitats. While there have been a number of studies that have included physical carbon flow estimates in the context of ecosystems services, the level of detail provided is not of a sufficient level required to support meaningful estimates for use within a carbon stock account.

Aquatic ecosystems

There is currently a lack of data to quantify the changes in the stock of carbon stored within the UK open water ecosystems. This will be investigated during the next process to update the ONS Freshwater Ecosystems Account.

Notes:

1. The UK Continental Shelf (UKCS) comprises those areas of the sea bed and subsoil beyond the territorial sea over which the UK exercises sovereign rights of exploration and exploitation of natural resources. (OGA, n.d.).

2. The EEZ extends from the baseline (mean low water mark) out to 200 nautical miles from the UK’s coast (UNCLOS, 2012).

3. The OGA is an executive agency sponsored by the Department of Energy and Climate Change (DECC).

4. Hard coal resources contains only bituminous coal and anthracite according to BGR classification.

5. At the NUTS 2 level.

6. Different types of coal have different carbon contents.

7. This is not a simultaneous movement to the addition.

8. Biomasse Energy Centre: Carbon emissions of different fuels.

9. Ajani & Comisari apply the following rates: condensate, 75%; LPG 77%; natural gas 74%.

10. Process by which vegetation is converted into the various grades of coal.

11. Also known as brown coal.

12. Ajani and Comisari, 2014: Figure determined as the average carbon content found in Australian coal stocks of anthracite, bituminous and sub-bituminous.

13. Geology.com (n.d.).

14. Priority Habitats are habitats that have been identified as a priority for conservation in the UK Biodiversity Action Plan.

15. DECC use data only down to one metre from the study.

16. Billett, M. F. Charman, D. J. Clark, J. M. Evans, C. D. Evans, M. G. Ostle, N. J, Worrall, F. Burden, A. Dinsmore, K. J. Jones, T. McNamara, N. P. Parry, L. Rowson, J. G. and Rose, R. 2010. Carbon balance of UK peatlands: current state of knowledge and future research challenges. Climate Research 45: 13-29.

17. Chapman SJ, Bell J, Donnelly D, Lilly A (2009) Carbon stocks in Scottish peatlands. Soil Use Management 25:105–112

18. Bradley RI, Milne R, Bell J, Lilly A, Jordan C, Higgins A (2005), A soil carbon and land use database for the United Kingdom, Soil Use Management 21:363–369.

19. Smith P, Smith J, Flynn H, Killham K and others (2007), ECOSSE: estimating carbon in organic soils—sequestration and emissions. Scottish Executive Environment and Rural Affairs Department, Edinburgh, www.scotland.gov, uk/Publications/2007/03/16170508/0.

20. The BioSoil Survey is a large EU soil and biodiversity survey in forestry, and is part of the programme of the Forest Focus regulation (2003–6). , The BoiSoil survey was the single largest soil monitoring exercise implemented so far at the EU scale.

21. Estimates only based on a soil depth of 15cm.

22. Standing waters include natural systems - such as lakes, meres and pools, and man-made waters such as reservoirs, canals, ponds and gravel pits.

23. Flowing waters include rivers and streams that flow into the sea or a lake.

24. Carbon sequestration refers to the removal of carbon from the atmosphere during the process of photosynthesis.

The presentation of the row entries in the account follows the basic form of the asset account in the SEEA Central Framework; the entries being opening stock, additions, reductions and closing stock. Additions to, and reductions in, stock have been split between managed and natural expansion and contraction.

There are six types of additions in the carbon stock account:

Natural expansion

Reflects increases in the stock of carbon over an accounting period due to natural growth. Effectively, this will be recorded only for biocarbon and may arise from climatic variation, ecological factors such as reduction in grazing pressure, and indirect human impacts such as the CO2 fertilisation effect (where higher atmospheric CO2 concentrations cause faster plant growth). Soils (the major biocarbon store) have a carbon equilibrium that, when reached, mean a habitat C stocks will plateau.

Managed expansion

Reflects increases in the stock of carbon over an accounting period due to human-managed growth. This will be recorded for biocarbon in ecosystems and accumulations in the economy, in inventories, consumer durables, fixed assets and waste stored in controlled landfill sites, and also includes greenhouse gases injected into the earth. The displacement effect, where carbon stocks increase due to proactive management in one area (i.e. via agricultural environment schemes) may result in increased productivity elsewhere, and, therefore, a reduction in its respective stock.

Discoveries of new stock

Encompasses the emergence of new resources added to a stock, which commonly arise through exploration and evaluation. This applies mainly, and perhaps exclusively, to geocarbon.

Upward reappraisals

Reflect changes due to the use of updated information permitting a reassessment of the physical size of the stock. The use of updated information may require the revision of estimates for previous periods so as to ensure a continuity of time series.

Reclassifications of carbon assets

Generally occurs in situations where another environmental asset is used for a different purpose. For example, increases in carbon in semi-natural ecosystems following the establishment of a national park on an area previously used for agriculture would be offset by an equivalent decrease in agricultural ecosystems. In this case, it is only the particular land use that has changed, that is, reclassifications may have no impact on the total physical quantity of carbon during the period in which they occur.

Imports

Recorded to enable accounting for imports of produced goods (e.g., petroleum products). Imports are shown separately from the other additions so that they can be compared to exports.

There are six types of reductions recorded in the carbon stock account:

Natural contractions

Reflect natural losses of stock during the course of an accounting period. They may be due to changing distribution of ecosystems (e.g., a contraction of natural ecosystems) or biocarbon losses that might reasonably be expected to occur based on past experience. Natural contraction includes losses from episodic events including drought, some fires and floods, and pest and disease attacks, and also includes losses due to volcanic eruptions, tidal waves and hurricanes.

Managed contractions

Relate to reductions in stock due to human activities and include the removal or harvest of carbon through a process of production. This includes mining of fossil fuels and felling of timber. Extraction from ecosystems includes both those quantities that continue to flow through the economy as products (including waste products) and those quantities of stock that are immediately returned to the environment after extraction because they are unwanted e.g. felling residues. Managed contraction also includes losses as a result of a war, riots and other political events; and technological accidents such as major toxic releases.

Downward reappraisals,

Reflect changes due to the use of updated information that permits a reassessment of the physical size of the stock. The reassessments may also relate to changes in the assessed quality or grade of the natural resource. The use of updated information may require the revision of estimates for previous periods to ensure a continuity of time series.

Reclassifications

Generally occur in situations where another environmental asset is used for a different purpose. For example, decreases in carbon in agricultural ecosystems following the establishment of a national park on an area used for agriculture would be offset by an equivalent increase in semi-natural ecosystems. In this case, it is only the particular land use that has changed; that is, reclassifications have no impact on the total physical quantity of carbon during the period in which they occur.

Exports

Recorded to enable accounting for exports of produced goods (e.g., petroleum products). Exports are shown separately from the other reductions so that they can be compared to imports.

Catastrophic losses,

Shown as a single entry, but are allocated between managed contraction and natural contraction. Catastrophic losses in managed contraction would include fires deliberately lit to reduce the risk of uncontrolled wild fires. For the purposes of accounting, reductions due to human accidents, such as rupture of oil wells, would also be included under managed contraction. Catastrophic losses could, however, be separately identified.

The SEEA-EEA recommends including accumulations of carbon in the economy in its carbon stock account. Accumulations in the economy (AIE) refer to the stocks of carbon stored within products produced through economic activity. Due to a range of conceptual and data limitations no attempt has been made to produce estimates of AIE in this article. It should be noted, however, that carbon related to AIE are small relative to geocarbon and biocarbon stocks. The following section outlines factors that should be taken into account when developing AIE estimates.

The SEEA applies the accounting concepts, structures, rules and principles of the System of National Accounts (SNA)¹. Through using this approach, the anthropogenic (human-created) stockpiles of carbon bearing materials generated through economic activity can be disaggregated and organised into categories based on the SNA. These are outlined in Table B below:

Accounting for the carbon contained in waste products follows the conventions of the SEEA-CF (SEEA-EEA, 2012). Only waste products deposited and stored in managed landfill sites are treated as being part of the economy. Non-managed waste deposit sites are excluded from the AIE scope. Another consideration when accounting for waste relates to the stocks of carbon created through geosequestration. Geosequestration involves the capturing of atmospheric CO2 from significant point sources i.e. coal burning power stations, and burying it securely underground. Such carbon stocks are also accounted for as part of the waste sector.

In order to maintain consistency across our natural capital accounts, the carbon stock account should employ the approach taken in the Farmland Ecosystems account and place livestock within the AIE category, while trees² and other cultivations will be treated as being within the environment (biocarbon). For geocarbon, the boundary at which the product crosses into the economy is the point before (materials in resources) reservoirs containing geocarbon are extracted (mined).

Imports and exports of carbon

Imports and exports of carbon are directly connected to AIE, in that they are another form of anthropogenic carbon stocks created through economic activities. Reference Table 1 includes additional rows for imports and exports. Imports are recorded to enable accounting for the carbon contained in the imports of produced goods (e.g., paper products) into the economy. Exports are recorded to enable accounting for the carbon contained in the exports of produced goods (e.g., petroleum products) out of the economy. Imports and exports are presented separately in the carbon stock account to enable comparison between the respective categories.

Notes:

1. The System of National Accounts (SNA) is the internationally agreed standard set of recommendations on how to compile measures of economic activity (UNSD, 2016).
2. This is because the UK does not have a concept of ‘plantations’, since in theory almost all woodland is available for timber irrespective of whether is has been naturally regenerated.

The atmosphere and oceans are the receiving environments for carbon released from the primary reservoirs (biosphere or geosphere) and Accumulations in the economy.

Measuring the carbon stock of, and flows between, the atmospheric and oceanic carbon pools is an important but complex aspect of environmental accounting. The oceans represent the globe’s largest reservoir (World Ocean Review, 2015) containing approximately 37,500 gigatons of carbon (GtC). This represents about fifteen times as much carbon present as is within Earth’s terrestrial biosphere¹ (2,477 Gt, IPCC 2000). The global store of carbon within the atmosphere was approximately 836 GtC in 2012 (CDIAC, n.d.). This is considerably higher than atmospheric carbon levels at the start of the industrial era (c.1750); global stocks are estimated to have been in the region of 592 GtC at that time.

Trace carbon gases in the atmosphere (or residuals) can be sourced from carbon pools within the biosphere or geosphere and from indirect flows via the economy. The main carbon bearing trace gases in the atmosphere are CO₂, methane (CH4) and carbon monoxide (CO), with CO₂ having by far the dominant representation². The IPCC report - Climate Change 2013: The Physical Science Basis reports the 2011 stock of CO₂ within the global atmosphere to have a mass equal to c.828 GtC; methane CH₄ to have a mass equal to c.3.7 GtC; and CO to have a mass equal to c.0.2 GtC. Emissions to the atmosphere from the geosphere are effectively one way and therefore relatively easy to account for.

Accumulations of atmospheric carbon are the most accurately measured quantity in the global carbon cycle (Global Carbon Budget). They result from both anthropogenic and natural processes. Estimates of atmospheric carbon stocks can be crudely derived by combining the concentration of carbon dioxide (CO₂) and other trace carbon gases (in parts per million) in the atmosphere with data on the total volume of the atmosphere (Vardon, 2014).

Carbon in the oceans is commonly estimated through calibrated modelling (Ajani & Comisari, 2014). Researchers have developed a variety of methods to quantify the present role of the oceans in the carbon cycle, however, comprehensive estimates remain a challenge. McNeil (2006) states that “while the ocean within each exclusive economic zone (EEZ) has a vast capacity to absorb anthropogenic CO₂ ... it is not mentioned within the Kyoto Protocol most likely due to inadequate quantitative estimates.” Measuring the change in the amount of dissolved inorganic carbon in the oceans is similarly difficult because the annual increase is small compared to the regional and temporal variability. While some broad based estimates exist for the flows into and out of the atmospheres and oceans (Global Carbon Project, 2015), there remain large gaps in knowledge.

The SEEA-CF excludes the ocean and the atmosphere from its measurement scope under the rationale that ‘the associated volumes of water and air are too large to be meaningful for analytical purposes at the country level’. Although ecosystem accounting is the focus of SEEA-EEA, the accounting framework lists important differences in ecosystems for ecosystem accounting purposes and the wider needs of the users of carbon stock information (Ajani & Comisari, 2014). Even so, there remain significant knowledge gaps and as such broadening the scope of SEEA consistent carbon accounts to include information on atmospheric and oceanic carbon is challenging.

Notes:

1. Global carbon stocks in vegetation and soil carbon pools down to a depth of one metre.
2. Other related gases include perfluorocarbons (PFCs), hydrofluorocarbons (HFCs) and non-methane volatile organic compounds (NMVOCs).

The following Net Present Value (NPV) formula is used to calculate the monetary asset value for UK ecosystems providing carbon sequestration services:

Net Present Value equation

Source: Office for National Statistics

Download this image Net Present Value equation

.png (1.5 kB)

The Net Present Value (NPV) equation is used to calculate the sum of discounted resource rents.

Where:

N = total number of periods (50 years)

t = year

r = social discount rate (SDR, 3.5% up to 30 years declining to 3.0% thereafter).